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25. SOIL TEMPERATURES BY YEAR

Soil temperatures are shown at depths of 30cm and 100cm below the surface, also the air temperature, averaged over the whole year.  The soil temperatures are on average about 0.8degC higher than the air temperature, and there was a steady increase in all three temperatures over the 49 years.

26. SOIL TEMPERATURES BY MONTH

Soil temperatures are shown at depths of 30cm and 100cm below the surface, also the air temperature, averaged over the each month (month 1 = Jan, 2 = Feb .....12 = Dec).  

There are differences in the temperatures at different depths, due to changing air temps, solar radiation on the surface, moisture.

The deeper you go, the flatter the curve is, so the temperature remains steadier as you go down into the soil.

Also, the peak in the air temp is around July-August, but the peak temp is generally later as you go down, as the summer surface heating takes time to propagate downwards through the soil. Likewise, the coolest air temp is around Dec-Jan, but the minimum at 100cm is again later, into February, due to the time it takes for the soil to cool down in the winter.

27. SOIL TEMPERATURES VARIATION BY DEPTH AND DAY EXAMPLE FEB MAR 2005

As air temperature varies, so the temperatures at different depths changes, but there is a delay as the rise/fall takes time to propagate down through the soil layers. In the example below, showing part of Feb and Mar 2005,  the rising air temperature from 9th-12th Feb is reflected in the rise at lower levels. As the air temperature fell suddenly on 13th Feb, it can be seen that the temperature at 10cm takes only a day or so to fall, but the temperature at 30cm and 100cm takes many days to stabilise at its lower value.